1. Field of the Invention
The present invention relates to fluid pump apparatus and more specifically to those magnetically levitating an impeller to discharge fluid such as blood.
2. Description of the Background Art
FIG. 18 is a vertical cross section of a magnetically levitated (maglev) pump apparatus and a block diagram of a controller thereof. In FIG. 18 a maglev pump apparatus 100 is configured with an electromagnet unit 120, a pump unit 130 and a motor unit 140 housed in a cylindrical housing 101. Electromagnet unit 120 has an electromagnet 121 and a position sensor 122 incorporated therein. Housing 101 has on one side a side wall having a center provided with an inlet 102 introducing a fluid. At least three electromagnets 121 and at least three position sensors 122 surround inlet 102.
In pump unit 130 an impeller 131 is rotatably housed and it has a portion closer to electromagnet unit 120, or closer to one side, that is supported by electromagnet 121 contactless through a partition 103, and position sensor 122 senses the distance as measured from one side of impeller 131. Impeller 131 has the other side with a permanent magnet 132 buried therein. Motor unit 140 houses a motor 141 and a rotor 142. Rotor 142 has a surface facing pump unit 130 and having a permanent magnet 143 buried therein opposite to permanent magnet 132 of impeller 131 with a partition 104 posed therebetween.
In the maglev pump apparatus thus configured, position sensor 122 provides an output which is in turn input to a sensor circuit 301 included in a controller 300 and sensor circuit 301 detects the distance between one side of impeller 131 and position sensor 122. Sensor circuit 301 provides an output which is in turn input to a PID compensator 302 to provide PID compensation and PID compensator 302 provides an output which is in turn amplified by a power amplifier 303 and thus applied to electromagnet 121 to control attractive force exerted toward the opposite side of impeller 131.
Furthermore impeller 131 has a portion closer to motor unit 140 that is affected by the attractive force exerted by permanent magnets 132 and 143 and impeller 131 is magnetically levitated by a non-controlled bearing provided by permanent magnets 132 and 143 and a controlled bearing provided by electromagnet 121 and it is rotated by the driving force of a motor 141 to allow blood or any other similar fluid introduced through inlet 102 to be output through an outlet (not shown) formed at pump unit 130.
In the FIG. 18 maglev pump 100 when a command is issued to provide levitation via the magnetic bearing, i.e., when attractive force occurs at electromagnet 121, as shown FIG. 19, impeller 13 moves from a position A, corresponding to an internal wall surface closer to motor 140 affected by a significant attractive force created by permanent magnets 132 and 143 configuring magnetic-coupling, to a normal levitation position B. However, because of over-shoot of an excessive response as impeller 131 levitates, impeller 131 exceeds normal position B and impinges against a position C corresponding to an internal wall surface closer to electromagnet unit 120, as represented in FIG. 19. Thereafter impeller 131 moves to normal levitation position B. If impeller 131, a target of position sensor 122, impinges on a wall surface and have its surface damaged, the sensing function may be impaired.
Furthermore if the apparatus is used as a blood pomp impeller 131 is housed in pump unit 130 having its inner wall surface coated with heparin to prevent formation of thrombosis and if impeller 131 impinges against the inner wall of the pump chamber the coating would be disadvantageously peeled off.
Therefore a main object of the present invention is to provide a maglev pump capable of preventing an impeller from impinging against an inner wall of a pump chamber when a command is issued to provide magnetic levitation.
The present invention provides a maglev pump including: a pump unit outputting a fluid through revolution of a rotative member in a casing; a drive unit magnetically coupled with the rotative member without contacting the rotative member, to rotate the rotative member; a position detection unit detecting a position of the rotative member as the rotative member levitates; and a controlled magnetic bearing unit operative in response to an output of the position detection unit to support the rotative member without contacting the rotative member, and it is characterized in that it is provided with a control means controlling a command signal of the controlled magnetic bearing unit to allow the rotative member to have a position closer to the drive unit when the rotative member starts magnetic levitation.
Thus in the present invention the rotative member can be prevented from impinging against an internal wall of the housing when a command is issued to provide magnetic levitation. Thus the internal wall of the housing can be protected from damage.
Preferably in magnetic levitation the control means shifts the signal output of the position detection unit gradually to a normal value.
More preferably the control means gradually shifts the signal output from the position detection unit in a direction opposite to a normal value to terminate magnetic levitation.
More preferably the maglev pump configures a blood pump.
More preferably the drive unit is switchable between a mode controlling a revolution rate to be constant and a mode controlling a current to be constant and the control circuit controls a revolution rate to be substantially constant when one of the modes is switched to the other of the modes.
Furthermore the control circuit controls a revolution rate within a tolerance of approximately xc2x120% when one of the modes is switched the other of the modes.
Furthermore the pump includes an adjustment circuit adjusting the position of the rotative member as the rotative member levitates after the maglev pump has been assembled.
The adjustment circuit periodically moves the rotative member in the casing axially.
Furthermore the adjustment circuit includes: a periodical signal generation circuit generating a periodical signal of a low frequency and applying the periodical signal to a circuit portion of the controlled magnetic bearing unit; and a correction circuit outputting a correction signal to the control circuit to rotate the rotative member in the casing at an axially center position, in response to the output from the position detection unit when the rotative member periodically moves according to the periodical signal output from the periodical signal generation circuit.
The periodical signal generation circuit generates a periodical signal of no more than 1 Hz to periodically move the rotative member.
The present invention in another aspect provides a maglev pump including: a pump unit having in a casing a rotative member rotated to output a fluid; a support supporting the rotative member; a drive unit rotating the rotative member; and a control circuit controlling and thus preventing the rotative member from having a revolution rate varying when a supplied power supply voltage varies while the rotative member is rotating in a mode controlling a current to be constant.
Preferably the control circuit adjusts a value of a command indicative of the mode according to the supplied power supply voltage and a feedback signal proportional to a value of a current fed to the drive unit.
More preferably the power supply voltage is supplied by switching between a direct current voltage converted from an alternating current voltage and a direct current voltage supplied from a battery.
The power supply voltage is a selected and further converted one of the direct current voltage converted from the alternating current and the direct current voltage supplied from the battery.
Still more preferably, the support is coupled with the rotative member magnetically without contacting the rotative member, and the maglev pump further includes: a position detection unit detecting a position of the rotative member as the rotative member levitates; and a controlled magnetic bearing operative in response to an output of the position detection unit to support the rotative member without contacting the rotative member.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.